The present invention relates to a molecular recognition type chemical charge coupled device (CCD) capable of measuring an ultramicro chemical substance with an ultrahigh sensitivity at a molecular level.
In recent years, it has been required that an environmental pollutant such as dioxin or environmental hormone and protein such as a DNA are measured at a ppb (parts per billion) or ppt (parts per tera) level. The environmental pollutant such as dioxin or environmental hormone should be measured by ultrahigh sensitivity analysis because an ultramicro substance is to be measured.
As a method of measuring ultramicro dioxin or environmental hormone, an SAW (surface acoustic wave) device method and a surface plasmon method have been studied. In the former method, an object to be measured is caused to come in contact with a surface elastic wave device and is measured based on a shift of a resonance frequency, which has a very high universality. It is apparent that analysis of 1 ng (nanogram), that is, in order of 1 ppb can be carried out with a frequency shift of 0.1 Hz. The latter method utilizes light transmission from the inside of an optical material to the outside. In any of the methods, the measurement can be carried out with a high sensitivity. However, an expensive device such as an electronic circuit or an optical system is required over the whole measuring system for operating the device.
For example, DNA measurement has been carried out in the following manner. More specifically, sections of approximately 10 mm square are formed on the surface of a slide glass. Hundreds to hundred thousands of fixed regions having a size of 10 xcexcm2 including different probe DNAs from each other are arranged two-dimensionally in one section. One section acts as a DNA chip and has a size of 10 cm2. A chip surface is immersed in and washed with a solution containing a target DNA previously subjected to a labeling treatment with a fluorescent material, and the target DNA complementary to the probe DNA is hybridized (associated) to remain on a surface. The hybridized DNA chip surface can be measured as a fluorescent image through a fluorescent laser microscope and a CCD camera, and automatic control is carried out by a computer to perform a data processing. There has also been software in which genes to correspond to positions of a light emitting spot are previously registered in the computer, a fluorescent material for emitting green and red lights having a resolution of 1 to 10 xcexcm is used to detect a feeble fluorescent intensity when forming a labeling piece, and hybridization profiles such as green and red signals or a yellow signal for double light emission can be compared in the same DNA chip.
However, the conventional method of measuring a DNA is based on a fluorescence method. The DNA to be measured is not directly measured. Therefore, there is a problem in that measuring precision basically depends on a conversion ratio. In addition, an expensive large-scale optical system is used. Therefore, there is a problem in that the whole device is expensive and large-sized.
In order to selectively and easily measure the object, a method of detecting a change in an electric potential of a functional substance as an ion selective electrode is the most effective. Examples of a method of directly and selectively measuring the substance to be measured include a mold polymerizing method (a molecular imprinting method). This method is also referred to as the mold polymerizing method in which a polymeric resin (host) and a substance to be measured (guest) are complexed and polymerized, and the guest is then removed to form a mold having a cavity in a portion of the host where the guest was present, and only molecules corresponding to the mold are taken out.
Examples of a method obtained by developing the mold polymerizing method include an interface mold polymerizing method. In the interface mold polymerizing method, a mold is formed on an oily water interface of a heterogeneous system in which a water layer and an oil layer are present together. The reaction to guest molecules does not reach the inside and is restricted to an interface. Therefore, there is an advantage that mass transfer is rapidly carried out and a response speed is higher than that of the ordinary mold polymerizing method.
In an electrochemical method, a change in a contact with environment pollution molecules can be directly taken as a signal. A large number of methods have been developed as a semiconductor sensor. In order to monitor an environmental polluting molecular concentration and to carry out remote sensing, the development of a gene manipulation technique of a microorganism and a useful function material is insufficient. For example, the remote sensing premises the field installation of an electronic device and plural sensing operations are required for real-time measurement.
There is a higher possibility that two-dimensional sensing might consequently obtain a new knowledge than the acquisition of an ultrahigh sensitivity of one sensor. According to simple calculation, it is possible to obtain a two-dimensional image signal including positional information in which face arrangement sensors of 4096, 16384 and 65536 correspond to a sensor in the two-dimensional sensing of 64xc3x9764, 128xc3x97128, and 256xc3x97256.
Furthermore, a technique for measuring bioimaging of molecules and cells has recently been developed remarkably. It is supposed that a device (chemical CCD) for transferring, through a CCD, electrochemical double layer surface charges generated on an interface between the environmental pollutant and the sensor will enable real-time two-dimensional chemical image measurement in the future. For the chemical CCD, it is proposed xe2x80x9cMethod and Apparatus for Measuring Physical Phenomenon or Chemical Phenomenonxe2x80x9d in Japanese Patent Application No. Hei 9-157716 filed dated on May 29, 1997. The same has published as JP-A-10-332423 or EP-A-0881486. The structure and operation principle of the chemical CCD according to the patent application will be described below with reference to FIGS. 7 to 9.
In FIG. 7, the reference numeral 1 denotes a chemical CCD having the following structure. More specifically, the reference numeral 2 denotes a semiconductor substrate comprising p-type Si (silicon), for example, and has a thickness of approximately 500 xcexcm. The semiconductor substrate 2 is provided with a channel stopper 3, a charge supply section 4, a charge injection adjusting section 5, a sensing section 6 to be a charge converting section, a barrier section 7, a charge transfer section 8, a floating diffusion 9, a reset gate 10, a reset drain 11, and an output transistor 12 having an MOS structure.
A sensor section 13 is formed by each of the charge supply section 4, the charge injection adjusting section 5, the sensing section 6 and the barrier section 7. The sensing section 6 is formed of a potential well constituted to change a depth corresponding to a chemical quantity, which will be described below in detail. Moreover, an output section 14 is formed by each of the floating diffusion 9, the reset gate 10, the reset drain 11 and the output transistor 12.
As shown in FIG. 8, the sensor sections 13 are arranged two-dimensionally to form an array. Thus, information on plural points can be fetched at the same time and signals on the points can be processed in order through the charge transfer section 8 and the output section 13. As shown in FIG. 8, the upper surface of the chemical CCD 1 includes a plurality of sensor sections 13 for converting a chemical phenomenon, for example, pH to electric charges, the charge transfer section 8 for transferring the electric charges obtained by the conversion in the sensor sections 13 in a direction of an arrow, and the output section 14 for converting the transferred electric charges into output signals, and the charge transfer section 8 includes a horizontal CCD 8H and a vertical CCD 8V.
The principle of measurement of the chemical CCD 1 will be described below with reference to a potential diagram of FIG. 9. For the measurement, a pulse voltage is applied to the charge supply section 4, the barrier section 7 and the reset gate 10, while a DC voltage is applied to electrodes other than the floating diffusion 9.
In an ordinary MOS structure using a p-type semiconductor, there has been known the fact that a depletion layer is formed on an interface between an insulating film and a semiconductor depending on a positive voltage to be applied to a metal electrode. By using this phenomenon, a potential state is set in the vicinity of the interface of the semiconductor and the insulating film as shown in FIG. 9.
In a state 1, the electric potential of the charge supply section 4 is set to be high (in a direction of an arrow) and electric charges 15 are not injected into the sensing section 6 as shown in FIG. 9A.
In a state 2, the electric charges 15 are injected into the sensing section 6 by reducing the electric potential of the charge supply section 4 as shown in FIG. 9B.
In a state 3, electric charges 15a taken out by the charge injection adjusting section 5 are accumulated in the sensing section 6 by increasing the electric potential of the charge supply section 4 as shown in FIG. 9C.
In a state 4, the electric charges 15a accumulated in the sensing section 6 are transferred to the floating diffusion 9 by increasing the electric potential of the barrier section 7 as shown in FIG. 9D.
In a state 5, all the electric charges 15a of the sensing section 6 are transferred to the floating diffusion 9 to close the barrier section 7, thereby stopping the flow of the electric charges as shown in FIG. 9E. In this stage, the electric potential of the floating diffusion 9 is determined by the quantity of the electric charges 15a thus transferred. Therefore, the electric potential is input to a gate section of the output transistor 12 having the MOS structure, a drain current of the output transistor 12 is measured by a source follower circuit, for example, and the output is sent to a signal processor having a data processing function and an image processing function, for example, a computer (not shown).
In a state 6, the electric potential of the floating diffusion 9 is read and the reset gate 10 is then turned on to reset to the electric potential of the reset drain 11 as shown in FIG. 9F. By the resetting, the same state as the state 1 is returned again. In other words, the electric charges can be output to the outside by repeating the operations of the states 1 to 6.
As is understood from the description with reference to FIG. 9, in the chemical CCD 1, the potential well (sensing section 6) constituted to change a depth corresponding to the chemical quantity is formed on the semiconductor substrate 2, the electric charges 15 are injected into the potential well 6 and the physical or chemical quantity is converted into electric charges corresponding to the size of the potential well. Thus, the scale of a chemical phenomenon is measured. According to the chemical CCD 1, the chemical phenomenon in a plurality of different positions can be measured at the same time. Since the chemical quantity is converted into the electric charges, the one-dimensional distribution or two-dimensional distribution of the chemical phenomenon can easily be formed into an image.
The invention has been made in consideration of the foregoing and has an object to provide a novel and useful molecular recognition type chemical CCD capable of measuring an ultramicro chemical substance with an ultrahigh sensitivity at a molecular level.
In order to achieve the object, the invention provides a molecular recognition type chemical CCD in which a molecular recognition layer is formed on a sensor face of a chemical CCD having such a structure that a plurality of potential wells constituted to change a depth corresponding to a chemical quantity are arranged two-dimensionally, electric charges are injected into the potential wells, and the chemical quantity is converted into an electric charge corresponding to the sizes of the potential wells.
For example, in the case in which the molecular recognition layer is formed by a molecule imprinting method, concentrations of various chemical substances including an environment pollutant such as dioxin or environmental hormone can be measured with a high sensitivity at a molecular level. If the molecular recognition layer can individually recognize various kinds of chemical substances, they can be detected at the same time.
According to the third aspect of the invention, moreover, the molecular recognition layer is constituted by a DNA complementary to a DNA to be measured. Thus, the DNA to be measured can be detected with a high sensitivity.
According to the fourth aspect of the invention, in the case in which a gel having a solution containing a substance to be measured mixed into a gel material for migration is provided on an upper surface of the molecular recognition layer and a DC voltage is applied to the gel to measure the substance to be measured in the gel which is obtained after electrophoresis, the substance to be measured can be measured in a separation state.